A conventional method for forming a multilayer interconnection includes a wiring forming step, and a contact hole forming step. In each of a wiring forming step and a contact hole forming step, a deposition step, a photolithography step, an etching step, and a removing step are carried out.
The conventional method for forming a multilayer interconnection is described hereinafter with reference to FIGS. 17(a) through (j). FIGS. 17(a) through (j) are cross sectional views illustrating each step of the conventional method for forming a multilayer interconnection.
As illustrated in FIG. 17(a), in the conventional method for forming a multilayer interconnection, a sputtering film 102 is formed on a glass substrate 101 by sputtering technique. This sputtering film 102 is a lower layer wiring section. After that, as illustrated in FIG. 17(b), in order to process the sputtering film 102 into a desired shape, a photoresist 103 in the desired pattern is arranged to cover on the sputtering film 102 (photolithography step). Then, as illustrated in FIG. 17(c), the sputtering film 102 is etched along the pattern of the photoresist 103 (etching step). Furthermore, as illustrated in FIG. 17(d). the photoresist 103 is removed (removing step). In this way, the sputtering, film 102 (lower layer wiring section) in the desired shape is formed on the glass substrate 101.
Then, on the sputtering film 102 (lower layer wiring section) formed on the glass substrate 101, a contact hole to connect the lower layer wiring section with an upper layer wiring section is to be formed. As illustrated in FIG. 17(e), in an insulating film deposition step, an insulating film 104 is formed to cover the sputtering film 102. Then, as illustrated in FIG. 17(f), in order to form the contact hole at a desired position in the insulating film 104, a photoresist 105 in a desired pattern is arranged to cover the insulating film 104 (photolithography step). After that, as illustrated in FIG. 17(g), the insulating film 104 is etched along the desired pattern of the photoresist 105, so that a contact hole 16 is formed (etching step). Furthermore, as illustrated in FIG. 17(h), the photoresist 105 is removed (removing step).
Moreover, after the removing step, as illustrated in FIG. 17(i), by sputtering technique, a wiring material is embedded into the contact hole 106 formed in the insulating film 104 (step of depositing wiring material for an embedded wiring). A layer made of the wiring material embedded into the contact hole 106 is an interconnection section 107 which connects an upper layer wiring section with the lower layer wiring section. And as illustrated in FIG. 17(j), an extra sputtering film formed on the insulating film 104 in the step of depositing wiring material for an embedded wiring is removed by etching, so that the interconnection section 107 is revealed (etching back step). Furthermore, after the etching back step, an upper layer wiring section is formed on the insulating film 104, which is not illustrated here. In this way, the interconnection section which connects the lower layer wiring section with the upper layer wiring section is formed.
Another method for forming a multilayer interconnection except for the above conventional method, for example, is a method for forming a multilayer interconnection as disclosed in Patent Citation 1 (Japanese Unexamined Patent Application Publication No. 58-176949 published on Oct. 17, 1983). In the method for forming a multilayer interconnection disclosed in Patent Citation 1, a first metal wiring film is mesa etched to leave only a through hole section in a convex shape. After an organic film is applied to expose the convex section of the first metal wiring film, which is formed by mesa etching, a second metal wiring film is formed. Thus, in the interconnection section (the convex section) between the first and second metal wiring films, a highly reliable through hole interconnection can be formed without causing defects such as disconnection and the like.
As a method to form an interconnection section to connect an upper layer wiring section with a lower layer wiring section, the following method is proposed except for the method for embedding a wiring material into a contact hole.
As illustrated in FIGS. 18(a) through (c), in the proposed method, by inkjet technique, ink droplets made of a wiring material are dropped in a contact hole and baked, so that an interconnection section is formed.
However, the methods for forming a multilayer interconnection described above are facing the following problems.
In the method for forming a multilayer interconnection illustrated in FIGS. 17(a) through (j), the wiring material is embedded into the contact hole 106 by sputtering technique, so that the interconnection section 107 is formed. This contact hole 106 is a very narrow region. Therefore, as illustrated in FIG. 17(i), when the wiring material is embedded into the very narrow contact hole, a void or disconnection may be caused at the formed interconnection section 107 affected by foundations such as a shape of a cross section of the contact hole 106 or the like (becoming inverse tapered shape, or large aspect ratio). Therefore, the method for forming a multilayer interconnection illustrated in FIGS. 17(a) through (j), the void, disconnection, or the like can be caused at the interconnection section 107 between the upper layer wiring section and the lower layer wiring section, and the interconnection section 107 between the upper layer wiring section and the lower layer wiring section faces a problem of reliability.
In the method for forming an interconnection section by dropping ink droplets made of the wiring material in the contact hole by inkjet technique and baking the ink droplets, the interconnection section between the upper layer wiring section and the lower layer wiring section faces the problem of the reliability, too. A conventional shape of a contact hole, as illustrated in FIG. 18(a), is box shaped seen from the upper layer wiring section. When the ink droplets are dropped in such a box shaped contact hole and baked, a cross section of the interconnection section formed by baking becomes deformative as illustrated in FIG. 18(b). Thus, the connection with the upper layer wiring section is not sufficient at this interconnection section. Moreover, as illustrated in FIG. 18(c), when a contact hole is more deeply formed, the cross section of the interconnection section, formed by dropping and baking the ink droplets, is further deformed, and accordingly the connection with the upper layer wiring section is not sufficient.